In Region 2, the use of rootstock is very successful for mandarin, calamansi, sweet orange and pummelos, this is referred to as calamandarin. In the absence of calamandarin, the same stock as the scion could be used for pummelo, ladu mandarin and calamansi. However, rootstocks are very susceptible to foot rot and root rot when planted on heavy or clayey soils.
Suitability of rootstock for a certain environmental condition is a very important factor to be considered by growers. For heavier soils calamandarin has been tested to be a good rootstock for most commercial varieties and it performs just as well in lighter soils. Trifoliate rootstock is compatible for Satsuma mandarins.
Citrus can be propagated by budding, grafting and marcotting. For commercial production, propagation can be done asexually through shield or chip budding. Shield and chip budding is the union of a desired scion variety and a suitable rootstock. Grafting and marcotting also give satisfactory results, but these methods are wasteful for propagating materials. Thus, these are recommended only for small-scale propagation.
Select fruits that are well-matured and free from abnormalities.
Extraction of Seed and Preparation
- Wash the extracted matured seeds with water several times to remove adhering pulp.
- Remove floating seeds during washing, these are immature seeds.
- Spread the seeds thinly in old newspaper and air dry for one to two hours prior to seed sowing.
Care of Germinated Seedlings
The seeds germinate in three to four weeks after sowing.
- Spray the seedlings with copper fungicide every after two weeks.
- Excessive watering should be avoided.
- If seedlings appear to be weak or show signs of stunting, water or spray with urea solution at the rate of 180 grams per 3 gallons of water.
- Prepare seedplot with at least one meter wide to a length convenient to the farmer.
Sowing of Seeds
Sow the seeds as early as possible after its extraction. The seedbed should contain sand or sandy loam soil. Sow the seeds 2 cm apart at a depth of 1 cm. Treat the borders of the seedbed with insecticide to prevent the entry of ants.
Pricking the Seedlings in Seedplots and Polyethylene Plastic Bags
- After three to four months or when the seedlings are about 10 to 12 cm tall, they are ready for pricking. Select seedling of uniform height and cull those with goose necks or bent roots.
- Before pricking or transplanting, immerse the seedling roots for five minutes in a copper fungicide solution.
- Plant the seedlings at a distance of 6 inches between hills and 6 inches between rows. Reserve vacant space of 2 feet between four rows to serve as nursery working pathways.
- Plant the seedlings directly to polyethylene plastic bags with soil media containing sandy loam soil.
- Prepare the copper fungicide solution by mixing 3 tablespoons of copper fungicide per gallon of water.
Care of Rootstock Liners Before Budding
- Always keep the citrus stock liners in the nursery free of weeds.
- Spray once every two weeks with insecticides to control insect pests like leaf miner, leaf rollers, orange dog and other leaf cutting insects.
- Add copper fungicide to prevent the occurrence of diseases like scab, blight and damping-off.
- Apply ammonium sulfate or urea after every weeding. Under normal circumstance this is done every three weeks or once a month.
Desirable Characteristics of a Rootstock
- The rootstock should be compatible with the scion variety to have good growth, long life, good yield and good fruit qualities.
- The seeds should be readily available and preferably highly polyembryonic to get uniform seedlings, and with a high percentage of germination.
- The rootstock must be adaptable to a wide range of soil depth, texture, structure, pH, salinity, moisture, and nutrient supply.
In the Philippines, Calamandarin is the most commonly used rootstock for all citrus species. It is fairly resistant to Phytophthora foot rot and tolerant to virus diseases and it has excellent root system.
Selection of Scion Variety and Budwood
Carefully select parent trees from which budwood will be taken using the following criteria:
- a record of satisfactory production over a period of at least 5 years;
- free from systemic diseases affecting the veriety;
- true-to-type variety.
Collection of Budsticks/Scion and Propagation Procedure
- Rootstock liners are ready for budding within four to six months after lining out in the nursery or plant in polyethylene plastic bags.
- Obtain budsticks or scion for propagation from healthy trees of fruiting age, regular bearers, true to type as to horticultural and fruit character of variety, not showing any sign of yellowing or leaf mottling pattern in the foliage.
- Avoid getting budsticks from dwarf trees showing pocketed trunk and crooked primary branches since such trees are possibly infected with severe strains of Tristeza virus.
- Immerse the gathered budsticks in 1,000 parts per million of any antibiotic tetracycline compounds for one to two minutes then air dry for at least 5 to 10 minutes before budding or grafting.
Methods of Asexual Propagation
Budding is done when the seedling is at least 4 to 5 months old in the nursery.
Steps in Budding
- Clean the stem to remove dirt and clip-off the leaves.
- Make an inverted T-shaped incision on the stem of the stock about 10 to 20 cm above the ground. The cut should be deep enough to cut through the bark.
- Cut a bud-eye about 2 cm long with a thin slice of wood included from the budwood.
- Insert the bud-eye all the way in the inverted-T incision on the stock by pushing it upward until the bud-eye is covered by the bark of the stock.
- Wrap the union with plastic tape to prevent drying and promote contact between scion and stock. Tie starting at the base of the bud and continue upward so that each successive turn overlaps slightly the one below it. Secure the wrap slipping the free end of the tape under the last lap.
- Remove the tape 2 to 3 weeks after budding. If the bud looks fresh and green, the lower half of the tape is left intact until the bud starts to grow. When the budling is about 10 cm, loop the seedling stock to induce rapid growth. When the new shoot is well developed, the seedling rootstock is cut back to about 1 cm of the graft union. Cover the cut portion with any wood paint. Remove all other shoots appearing in the stock and only allow vigorous scion shoot to grow.
Continue to promote the development of the plant by doing the necessary cultural management practices such as weeding, cultivation, watering and fertilization. Spray appropriate insecticides every 2 weeks to avoid infestation of citrus psylla.
Grafting is done by joining together a rootstock and a scion until they unite permanently and continue their growth as one plant.
Steps in Grafting
- Select a healthy rootstock about the size of an ordinary lead pencil or slightly larger.
- Make a longitudinal cut at the center of the cut surface deep enough to accommodate the wedge that may be cut on the scion.
- After preparing the rootstock, select a healthy scion of the same size as the rootstock is about 10 to 15 cm long. Hold firmly and make a wedge about 4 to 5 cm long at the basal section.
- Insert the scion on the rootstock and secure firmly by wrapping a plastic tape around the joints.
- Cover the joints with plastic bag to protect the growth of the bud. Excessive moisture may rot the bud. Remove the plastic cover when the bud begins to grow.
Inarching is a method wherein the scion is made to unite with the rootstock while they are growing independently on their own root systems.
Steps in Inarching
- Select an active growing rootstock and bring it to a branch that approximates its size. Provide support to the rootstock like bamboo or wooden platforms.
- Cut the longitudinal section of the rootstock about 4 to 5 cm and about half its thickness. Make the same cut in the scion.
- Fit them together by tying firmly with a string or a plastic tape.
- When the union has taken place, gradually cut the scion below the point of union and cut the rootstock above the union. After a week, make a second cut. If the scion does not show any signs of wilting after the second cut, cut it off completely and plant directly.
Multiple Rootstock Propagation
This method is commonly used in orchards to rejuvenate old trees.
Steps in Multiple Rootstock Propagation
Cut a trunk of an old tree about two feet above the ground. Wait for the sprouts to reach pencil size.
- Select a branch from a certified parent tree with equal sizes and compatible species to be grafted or budded to the new sprouts.
- The scion and the stock must have a long, even slope and slightly hollowed cut, approximately 2 to 3 inches, for a better contact.
- Follow steps in budding/grafting or inarching as the case maybe.
Care of Asexually Propagated Plants
Budded seedlings must be watered and sprayed with insecticide and fungicide.
When the newly budded plant is a month-old, transfer newly balled plant in polyethylene bags under a nursery shed for acclimatization.
- Water the newly potted plants.
- Spray foliar fertilizer one month after potting.
- Prune water sprouts below the bud union and spray insecticide mixed with fungicide.
- Potted plants are ready for planting in the field 3 months after potting.
Plants in polyethylene bags should be planted after hardening. For direct planting, the scion should be three-fourths the size of the rootstock or 30 to 40 cm tall. It is best to transplant with a ball of soil. The shape and size of the ball of soil that goes with the plant is determined by the size of the plant. A balling spade is a useful tool for balling plants.
The ball is wrapped with gunny sack, dried banana sheaths, or plastic bag to keep the soil intact. However, planting asexually propagated citrus in the field can be done by removing the soil and arranging the root system in place for easier root development.
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